Method for regulating the brake power on the wheels of a single-track vehicle and brake system for carrying out said method

ABSTRACT

The invention relates to a method for regulating the brake power on the wheels (VR, HR) of at single-track vehicle, using a brake system comprising a wheel brake circuit (RBKVR) having a pressure modulator (RGCVR) for regulating the brake pressure pVR on a front wheel brake ( 54 ); a wheel brake circuit (RBKHR) having a pressure modulator (RGVHR) for regulating the brake pressure pHR on a rear wheel brake ( 54 ′); at least one control circuit (STKHBZ, STKFBZ) for controlling both pressure modulators (RGVVR, RGVHR); and a control unit ( 94 ). According to the invention, the brake pressure pHR nominal in the brake circuit (RBKHR) for the rear wheel (HR) is determined according to the brake pressure pVR actual detected in the brake circuit (RBKVR) for the front wheel (VR)—taking an ideal brake power distribution characteristic stored in the control unit ( 94 ) as a basis—and is regulated for the rear wheel (HR) by means of the pressure modulator (RGVVR) in the wheel brake circuit (RBKHR). As a result, a method is provided which enables the best possible use of the grip between the tyres and the ground in an automated manner during a brake process. The invention also relates to a simply constructed brake system for carrying out the method.

FIELD OF THE INVENTION

[0001] The present invention relates to a method of controlling the braking force at the wheels of a single-track vehicle and to a brake system for implementing the method. In particular, the invention relates to a brake system for motorcycles, with which the two wheels may be braked independently of one another with the best possible grip close to or on the ideal brake force distribution curve.

BACKGROUND OF THE INVENTION

[0002] Vehicles of all types, whether single- or multi-track, undergo a change in the loading of the rear and front axles during braking and acceleration due to physical conditions and their structural features. The consequence is differences in grip and thus different braking actions at the rear and front wheels while braking forces there remain constant. These differences in grip may cause overbraking and consequently locking due to the changing, smaller load proportion at the rear wheel during braking, even before the maximum braking power for deceleration may be reached at the front wheels and effectively utilised. This causes track instability and may result in skidding or even swerving of the vehicle in the respective phase. It is thus often no longer possible even for experienced drivers to maintain control of the vehicle, in particular of a motorcycle.

[0003] such systems have no advantages over uncontrolled brake systems.

[0004] Furthermore, the conventional behaviour of motorcyclists, which is to actuate predominantly only one brake circuit, stands in the way of achieving both the best possible braking distance and uniform utilisation of the grip at the front and rear wheels. An improvement in this regard was achieved by the circuit (semi-integrated circuit) known from the Applicant's European patent no. EP-B-0 761 520, with which the ABS modulator at the rear wheel is activated automatically when the control valve (=ABS modulator) is actuated at the front wheel. However, even in the case of this improved, driver-relieving circuit arrangement for a non-muscular-energy-assisted brake device equipped with ABS, brake status-dependent variables are not taken into account, such that optimum grip utilisation, allowing the best possible deceleration while overcoming the influence of the driver, is impossible to achieve.

[0005] The above-described disadvantages have a serious effect on driver safety, in particular in the case of motorcycles, because

[0006] in a motorcycle both the static and dynamic axle loads may vary markedly more than in the case of a car,

[0007] the ratio of admissible total weight to kerb weight is higher, and

[0008] the ratio of centre of gravity height to wheel base is plainly greater and changes more markedly than in the case of a car with its small wheel load variations and large vibration absorber action, which greatly impairs cornering behaviour of a motorcycle despite its relatively small axle mass.

[0009] Furthermore, the conventional digital pressure regulation using on-off valves found in vehicle dynamics control systems is deemed a disadvantage since their load change impacts generate imbalance in the running gear, in particular when used in motorcycles.

[0010] In addition, DE-A-199 51 535 discloses a brake arrangement for a motorcycle, which comprises a hydraulically actuated front wheel brake and a hydraulically actuated rear wheel brake. The front wheel brake and the rear wheel brake each have a brake caliper with three pistons, of which one piston may be hydraulically loaded independently of the other two pistons. The one piston of the front wheel brake may be hydraulically pressurised via a first ABS pressure modulator from a lever main cylinder actuatable by means of a brake lever, while the one piston of the rear wheel brake may be hydraulically pressurised via a second ABS pressure modulator from a pedal main cylinder actuatable by means of a brake pedal. At the line portions between the lever main cylinder and the first ABS pressure modulator and between the pedal main cylinder and the second ABS pressure modulator there is in each case provided a pressure sensor, by means of which the actuation pressure generated in the lever main cylinder or the pedal main cylinder respectively may be detected. The pressure sensors are connected with an electronic control unit (ECU), via which a first hydraulically controlled actuator and a second hydraulically controlled actuator may be activated. The first actuator is a component of a further hydraulic circuit for hydraulically loading the other two pistons of the brake caliper of the front wheel brake, while the second actuator is a component of a further hydraulic circuit which serves in hydraulic loading of the other two pistons of the brake caliper of the rear wheel brake.

[0011] If the brake pedal is actuated independently, a hydraulic pressure from the pedal main cylinder acts via the second ABS pressure modulator on the one piston of the brake caliper of the rear wheel brake and the rear wheel is braked. At the same time, the corresponding pressure sensor detects the pedal actuation pressure and outputs it to the ECU. The ECU then carries out a calculation on the basis of this detection signal and outputs a control signal to the actuators, which hydraulically load the other two pistons of the brake caliper of the rear wheel brake and the other two pistons of the brake caliper of the front wheel brake in a suitably distributed manner and with given timing, in order to brake the front wheel and the rear wheel. More precisely, if the brake pedal is actuated, firstly the brake comes into contact with the rear wheel and, as the pedal is pressed further down, the hydraulic pressure of the rear brake is increased and, if it exceeds a set value, the brake comes into contact with the front wheel using the further hydraulic circuit, which comprises the first actuator. It is intended thereby to prevent brake diving of the motorcycle at the time of braking.

[0012] If the brake lever is actuated independently, hydraulic pressure from the lever main cylinder acts via the first ABS pressure modulator on the one piston of the brake caliper of the front wheel brake and the front wheel is braked. At the same time, the corresponding pressure sensor detects the lever actuation pressure and outputs it to the ECU. Then, on the basis of this detection signal, hydraulic pressure is fed to the other two pistons of the brake caliper of the front wheel brake and to the other two pistons of the brake caliper of the rear wheel brake by control of the first or second actuator respectively, and the braking force acts in a suitably distributed manner and with given timing on the front wheel and the rear wheel. If, in this situation, the brake pedal is then acted upon, hydraulic pressure is fed to the rear wheel brake from the pedal main cylinder via the second ABS pressure modulator, which hydraulic pressure acts additionally on the rear wheel. In order to prevent premature locking of the rear wheel in this case, the brake force fraction generated in the further hydraulic circuit comprising the second actuator is reduced appropriately.

[0013] This previously known brake arrangement has a relatively complicated structure, with its two brake circuits per wheel. Activation of the brake circuits is also complex. Furthermore, the best possible utilisation of the grip between tyre and ground is not possible in particular in the case of actuation of the brake pedal only, because in this case no braking action at all or only delayed braking action is generated at the front wheel as a function of the level of pedal actuation pressure.

[0014] Finally, a similarly complex brake system for motorcycles is revealed by EP-A-0 687 621. According to this prior art, two brakes are provided at the front wheel, each with a brake caliper, while one brake with a brake caliper is associated with the rear wheel, wherein each brake caliper comprises three pistons. To activate the brake system, there are provided on the one hand a lever main cylinder actuatable by means of a brake lever and on the other hand a pedal main cylinder actuatable by means of a brake pedal.

[0015] If only the brake lever is actuated, without the brake pedal being actuated, the front wheel brakes and the rear wheel brake are activated by the lever main cylinder. If, on the other hand, only the brake pedal is actuated, without the brake lever being actuated, the rear wheel brake and only one of the front wheel brakes are activated by the pedal main cylinder if the actuation force at the brake pedal is relatively small or the rear wheel brake and both front wheel brakes are activated if the actuation force at the brake pedal is relatively large. To this end, there is a direct active connection between the lever main cylinder and two pistons of each front wheel brake. Furthermore, the one front wheel brake is equipped with an auxiliary main cylinder, by means of which a hydraulic pressure may be generated by the braking reaction generated in accordance with actuation of this front wheel brake. The auxiliary main cylinder is in turn actively connected via a pressure reducing means with two pistons of the rear wheel brake. Finally, the pedal main cylinder is actively connected directly with the third piston of the rear wheel brake and the third piston of the front wheel brake, with which the auxiliary main cylinder is associated, while an active connection is produced with the third piston of the other front wheel brake via a pressure control means.

[0016] In contrast to the above-described prior art, the object of the invention is to provide a method of controlling the braking force at the wheels of a single-track vehicle, which allows the best possible automated utilisation of the grip between tyre and ground during braking, together with a simply designed brake system for implementing the method.

[0017] This object is achieved by the features indicated in claims 1 and 6 respectively. Advantageous or expedient further developments of the invention constitute the subject matter of claims 2 to 5 and 7 to 12.

SUMMARY OF THE INVENTION

[0018] According to the invention, in the case of a method of controlling the braking force at the wheels of a single-track vehicle using a brake system which comprises only one wheel brake circuit with a pressure modulator for adjusting the braking pressure at a front wheel brake, only one wheel brake circuit with a pressure modulator for adjusting the braking pressure at a rear wheel brake, at least one control circuit for activating both pressure modulators and a control unit, the braking pressure p_(RWnominal) in the rear wheel brake circuit is determined as a function of the braking pressure p_(FWactual) detected as a reference input variable in the front wheel brake circuit by means of a pressure sensor, on the basis of an ideal brake force distribution characteristic stored in the control unit, and is adjusted by the pressure modulator in the rear wheel brake circuit.

[0019] As a result, in the case of a semi-integrated brake system or a fully integrated brake system and using the braking pressure in the front wheel brake circuit as a reference input variable, the braking pressure in the rear wheel brake circuit is determined and adjusted automatically in accordance with the ideal brake force distribution, always starts at zero again when the ignition is turned “ON”, wherein the latter calculates the results of the first temperature function in such a way that it rises more sharply until the two temperature functions supply the same results.

[0020] With regard to the device, to implement the above method the invention provides a brake system for single-track vehicles, having only one front wheel brake circuit, which comprises a pressure modulator for adjusting a braking pressure applicable to a front wheel brake, only one rear wheel brake circuit, which comprises a pressure modulator for adjusting a braking pressure applicable to a rear wheel brake, a first control circuit, by means of which the two pressure modulators may be activated, a second control circuit, by means of which the two pressure modulators may be activated, and a control unit, in which an ideal brake force distribution characteristic is stored between front wheel and rear wheel and by means of which the pressure modulator in the rear wheel brake circuit may be activated, wherein a pressure sensor is provided in the front wheel brake circuit, by means of which pressure sensor the braking pressure p_(FWactual) may be detected in the front wheel brake circuit and which is connected with the control unit, wherein a braking pressure p_(RWnominal) for the rear wheel brake circuit may be determined by means of the braking pressure p_(FWactual) detected in the front wheel brake circuit as a reference input variable, on the basis of the ideal brake force distribution characteristic stored in the control unit, and wherein the determined braking pressure p_(RWnominal) for the rear wheel brake circuit may be adjusted by the pressure modulator activated by the control unit in the rear wheel brake circuit. Thus, both wheel brake circuits are advantageously also always activated upon braking, which results overall in better braking action.

[0021] An advantageous further development of the brake system provides that each pressure modulator comprises a valve body, which limits in controllable manner a restriction gap through which a hydraulic fluid is forced to flow during braking, in order to establish in a pressure chamber a defined dynamic pressure which may be applied to the respective wheel brake.

[0022] It is preferable for the valve body of each pressure modulator to be activatable electromagnetically and hydraulically via a control piston for adjustment of the restriction gap. The control piston of each pressure modulator may be displaced by the pressurisation of a control chamber and/or by mechanical loading via an activating piston guided slidingly in an activating chamber and loadable hydraulically via

[0023] temperature function F₂ supplying the recalculated temperature value T_(n) always starts at zero again when the ignition is turned “ON”, wherein the latter calculates the results T_(altn) of the first temperature function F₁ in such a way that it rises more sharply until the two temperature functions supply the same results again at T_(x). The reference numerals w and k indicate by way of example, with regard to the temperature function F₂, when energy is supplied (w) to the brake disk 62′ and when it is dissipated (k).

[0024] The above-described temperature model has on the one hand the advantage that a complex sensor system is not required to detect brake disk temperature. On the other hand, it advantageously manages without electronic components and time buffer elements which would remove power from the battery when the motorcycle was at a standstill. The latter advantage in particular means that this temperature model is also of interest for other applications in which a variable temperature needs to be determined computationally at a body which exhibits warming-up and cooling-down phases.

[0025] A method is disclosed of controlling the braking force at the wheels of a single-track vehicle using a brake system which comprises only one wheel brake circuit with a pressure modulator for adjusting the braking pressure p_(FW) at a front wheel brake, only one wheel brake circuit with a pressure modulator for adjusting the braking pressure p_(RW) at a rear wheel brake, at least one control circuit for activating both pressure modulators and a control unit. According to the invention, the braking pressure p_(RWnominal) in the rear wheel brake circuit is determined as a function of the braking pressure p_(FWactual) detected as a reference input variable in the front wheel brake circuit by means of a pressure sensor, on the basis of an ideal brake force distribution characteristic stored in the control unit, and is adjusted by the pressure modulator in the rear wheel brake circuit. As a result, a method is provided which allows the best possible automated utilisation of the grip between tyre and ground during braking. The invention also provides a simply designed brake system for implementing the method. 

1. A method of controlling the braking force at the wheels (FW, RW) of a single-track vehicle using a brake system which comprises only one wheel brake circuit (WBC_(FW)) with a pressure modulator (CV_(FW)) for adjusting the braking pressure (p_(FW)) at a front wheel brake (54), only one wheel brake circuit (WBC_(RW)) with a pressure modulator (CV_(RW)) for adjusting the braking pressure (p_(RW)) at a rear wheel brake (54′), at least one control circuit (CC_(HBC), CC_(FBC)) for activating both pressure modulators (CV_(FW), CV_(RW)) and a control unit (94), wherein the braking pressure (p_(RWnominal) in the wheel brake circuit (WBC_(RW)) for the rear wheel (RW) is determined as a function of the braking pressure (p_(FWactual)) detected as a reference input variable in the wheel brake circuit (WBC_(FW)) for the front wheel (FW) by means of a pressure sensor (90), on the basis of an ideal brake force distribution characteristic (FIG. 6) stored in the control unit (94), and is adjusted by the pressure modulator (CV_(FW)) in the wheel brake circuit (WBC_(RW)) for the rear wheel (RW).
 2. A method according to claim 1, wherein the brake force distribution characteristic (FIG. 6) stored in the control unit (94) comprises two ideal brake force distribution curves (f_(LSC0), f_(LSC1)), of which the one curve (f_(LSC0)) is representative of an unladen vehicle while the other curve is (f_(LSC1)) is representative of a vehicle under maximum load.
 3. A method according to claim 2, wherein a counter (LSC_(n)) representative of the actual loading of the vehicle is produced, which, taking account of the two ideal brake force distribution curves (f_(LSC0), f_(LSC1)), serves in calculating a pressure calculation variable (p_(LSC)) for a braking pressure (p_(FWactual)) detected in the wheel brake circuit (WBC_(FW)) for the front wheel (FW), which variable lies, in accordance with the actual loading of the vehicle, between or on one of the two ideal brake force distribution curves (f_(LSC0), f_(LSC1)), wherein the braking pressure (p_(RWnominal)) is determined for the rear wheel (RW) as a function of the calculated pressure calculation variable (P_(LSC)).
 4. A method according to one of the preceding claims, wherein the measured or calculated temperature (T_(n)) of the rear wheel brake disk (62′) is also taken into account in determining the braking pressure (p_(RWnominal)) for the rear wheel (RW), in such a way that the braking pressure (p_(RWnominal)) is reduced for the rear wheel (RW) when given temperature limits (T_(limit), T_(max)) are exceeded.
 5. A method according to claim 4, wherein, during calculation of the temperature of the brake disk (62′) with the ignition “ON”, two temperature functions (F₁, F₂) are always produced, of which the one temperature function (F₁) serves as an auxiliary function which, after the ignition has been turned “OFF” and “ON” again, always starts again at the last calculated temperature value (T_(altn−1)=T_(sp)) while the other temperature function (F₂) supplying the recalculated temperature value (T_(n)) always starts at zero again when the ignition is turned “ON”, wherein the latter (F₂) calculates the results (T_(altn)) of the first temperature function (F₁) in such a way that it (F₂) rises more sharply until the two temperature functions supply the same results (FIG. 8: at T_(x)).
 6. A brake system for single-track vehicles for implementing the method according to one of the preceding claims, having only one wheel brake circuit (WBC_(FW)) for the front wheel (FW), which comprises a pressure modulator (CV_(FW)) for adjusting a braking pressure (p_(FW)) applicable to a front wheel brake (54), only one wheel brake circuit (WBC_(RW)) for the rear wheel (RW), which comprises a pressure modulator (CV_(RW)) for adjusting a braking pressure (p_(RW)) applicable to a rear wheel brake (54′), a first control circuit (CC_()HBC)), by means of which the two pressure modulators (CV_(FW), CV_(RW)) may be activated, a second control circuit (CC_(FBC)), by means of which the two pressure modulators (CV_(FW), CV_(RW)) may be activated, and a control unit (94), in which an ideal brake force distribution characteristic (FIG. 6) is stored between front wheel (FW) and rear wheel (RW) and by means of which the pressure modulator (CV_(RW)) in the wheel brake circuit (WBC_(RW)) for the rear wheel (RW) may be activated, wherein in the wheel brake circuit (WBC_(FW)) for the front wheel (FW) there is provided a pressure sensor (90), by means of which the braking pressure (p_(FWactual)) may be detected in the wheel brake circuit (WBC_(FW)) for the front wheel (FW) and which is connected with the control unit (94), wherein, by means of the braking pressure p_(FWactual) detected as a reference input variable in the wheel brake circuit (WBC_(FW) for the front wheel (RW), on the basis of the ideal brake force distribution characteristic (FIG. 6) stored in the control unit (94), a braking pressure (p_(RWnominal) may be determined for the wheel brake circuit (WBC_(RW) for the rear wheel (RW), and wherein the determined braking pressure (p_(RWnominal)) for the wheel brake circuit (WBC_(RW)) for the rear wheel (RW) may be adjusted by the pressure modulator (CV_(FW)) activated by the control unit (94) in the wheel brake circuit (WBC_(RW)) for the rear wheel (RW).
 7. A brake system according to claim 6, wherein each pressure modulator (CV_(FW), CV_(RW)) comprises a valve body (16, 16′), which limits in controllable manner a restriction gap (18, 18′) through which a hydraulic fluid is forced to flow during braking, in order to establish in a pressure chamber (10, 10′) a defined dynamic pressure which may be applied to the respective wheel brake (54, 54′).
 8. A brake system according to claim 7, wherein the valve body (16, 16′) of each pressure modulator (CV_(FW), CV_(RW)) is activatable electromagnetically and hydraulically via a control piston (24, 24′) for adjustment of the restriction gap (18, 18′).
 9. A brake system according to claim 8, wherein the control piston (24, 24′) of each pressure modulator (CV_(FW), CV_(RW)) may be displaced by the pressurisation of a control chamber (20, 20′) and/or by mechanical loading via an activating piston (82, 82′) guided slidingly in an activating chamber (80, 80′) and loadable hydraulically via the activating chamber (80, 80′).
 10. A brake system according to claim 8 or claim 9, wherein the control piston (24, 24′) of each pressure modulator (CV_(FW), CV_(RW)) may be displaced by means of a solenoid actuator consisting of an armature on the control piston (24, 24′) and a solenoid (26, 26′).
 11. A brake system according to one of claims 6 to 10, wherein each wheel brake circuit (WBC_(FW), WBC_(RW)) is provided with a pressure sensor (90).
 12. A brake system according to one of claims 6 to 11, wherein each control circuit (CC_(HBC), CC_(FBC)) is provided with a pressure sensor (90). 